Ceramic on metal pressure transducer

ABSTRACT

A transducer apparatus is disclosed herein, including a method thereof for forming the transducer apparatus. A metal diaphragm can be molecularly bonded to a ceramic material to form a ceramic surface thereof. A bridge circuit is connected to the ceramic surface of the metal diaphragm. An input pressure port for pressure sensing thereof can then be provided, wherein the input pressure port is connected to the metal diaphragm to thereby form a transducer apparatus comprising the metal diaphragm, the bridge circuit and the input pressure port. The metal diaphragm is preferably welded to the input pressure. The metal diaphragm and the ceramic surface thereof preferably operate over a temperature of range of at least 40° C. to 150° C., as does the transducer apparatus. The transducer apparatus functions as a pressure transducer that can be used in corrosive media and high temperature applications.

TECHNICAL FIELD

Embodiments are generally related to sensing devices and methodsthereof. Embodiments are also related to pressure transducers.Embodiments are additionally related to pressure sensors. Embodimentsare additionally related to ceramic-on-metal and ATF (Advanced ThickFilm) processes and techniques.

BACKGROUND OF THE INVENTION

Various sensors are known in the pressure sensing arts. Pressuretransducers are well known in the art. One example of a pressuretransducer is a device formed with a silicon substrate and an epitaxiallayer, which is grown on the substrate. A portion of the substrate canthen be removed, leaving a thin, flexible diaphragm portion. Sensingcomponents can be located in the diaphragm portion to form a pressuretransducer. In operation, at least one surface of the diaphragm can beexposed to a process pressure. The diaphragm deflects according to themagnitude of the pressure, and this deflection bends the attachedsensing components. Bending of the diaphragm creates a change in theresistance value of the sensing components, which can be reflected as achange in the output voltage signal of a resistive bridge formed atleast partially by the sensing components.

Some techniques for forming a composite diaphragm for a pressuretransducer or similar device involve configuring a substrate layerhaving a first conductivity type, wherein the substrate layer includes afirst surface. Positive implants can then be deposited in the firstsurface of the substrate layer, and an epitaxial layer grown on thefirst surface of the substrate layer so that the positive implants formpositive diffusions in the epitaxial layer. An oxide pattern can be thenformed on the epitaxial layer, and a top layer deposited over theepitaxial layer and oxide pattern. The substrate layer and positivediffusions of the epitaxial layer can then be etched to form thecomposite diaphragm. Such a composite diaphragm can therefore beprovided for use in a pressure sensor or like device. The diaphragmcomprises a first layer of silicon nitride and a second layer attachedto the silicon nitride layer and comprising a pressure sensor pattern ofsilicon material.

Pressure transducers of the type which comprise a thin, relativelyflexible diaphragm portion of suitable material, such as silicon orceramic, on which either a selected resistive element or a capacitiveplate is printed whereby exposure to a pressure source causes deflectionof the diaphragm will cause a change in the resistive value of theresistive element or a change in the spacing of the capacitive platewith a mating capacitive plate and concomitantly a change in capacitanceare therefore well known in the art.

When used as a low pressure sensor, economical packaging of thetransducer in a housing so that an effective seal is obtained while atthe same time preventing stress related to the mounting and sealing ofthe transducer from influencing the output becomes problematic. This iscaused, at least in part, by the significant difference in thermalexpansion between the material used to form the transducer, e.g.,silicon, ceramic or the like, and the housing of plastic or the like. Aconventional sealing arrangement involves placement of a ring of sealingmaterial around an inlet pressure port in a housing and mounting thetransducer so that the pressure sensitive diaphragm is precisely alignedwith the pressure port. This conventional arrangement not only involvesstress isolation issues, it also limits flexibility in design choices indefining the location of the transducer within the package.

One of the major problems with such pressure transducer devices,including those that utilize diaphragm or diaphragm portionconfigurations, is that such devices are not reliable in corrosive andhigh-temperature applications. A need therefore exists for a low-costhigh accuracy pressure transducer that can be used in corrosive mediaand high-temperature applications.

BRIEF SUMMARY OF THE INVENTION

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

It is, therefore, one aspect of the present invention is to provide anapparatus and a method which overcomes the above noted prior artlimitations.

It another aspect of the present invention to provide an improved sensorapparatus and method.

It is an additional aspect of the present invention to provide for animproved transducer apparatus.

It is yet an additional aspect of the present invention to provide foran improved transducer apparatus, which can be formed utilizingceramic-on-metal and ATF (Advanced Thick Film) processes and techniques.

It is a further aspect of the present invention to provide for animproved method for connecting the flex circuit to the bridge circuit.

The aforementioned aspects of the invention and other objectives andadvantages can now be achieved as described herein. A transducerapparatus is disclosed herein, including a method thereof for formingthe transducer apparatus. A metal diaphragm is molecularly bonded to aceramic material to form a ceramic surface thereof. A bridge circuit isconnected to the ceramic surface of the metal diaphragm. An inputpressure port for pressure sensing thereof can then be provided, whereinthe input pressure port is connected to the metal diaphragm to therebyform a transducer apparatus comprising the metal diaphragm, the bridgecircuit and the input pressure port.

The metal diaphragm is preferably welded to the input pressure port. Themetal diaphragm and the ceramic surface thereof preferably operate overa temperature of range of at least approximately −40° C. to 150° C., asdoes the transducer apparatus. The ceramic material is molecularlybonded to the metal diaphragm to form the ceramic surface thereof. Theceramic surface bonded to the metal diaphragm can also be configured asa ceramic substrate. The ceramic surface provides corrosion protectionto the metal diaphragm. The bridge circuit generally comprises aresistor network and provides an output proportional to the appliedforce. A flex circuit comprising an ASIC (Application SpecificIntegrated Circuit), associated circuitry and EMI protection providessignal conditioning, calibration and compensation. A snap on connectorsystem comprising a plastic snap on lead frame and Z axis conductormaterial can be utilized for connecting the flex circuit to the bridgenetwork which is located on the diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 illustrates a top and side-sectional view of a transducerapparatus, which can be implemented in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment of the present invention and are not intended to limit thescope of the invention.

FIG. 1 illustrates a side-sectional view a transducer apparatus 100,which can be implemented in accordance with a preferred embodiment ofthe present invention. Transducer apparatus generally includes a metaldiaphragm 119 which is molecularly bonded to a ceramic material orceramic substrate 118. A bridge circuit 115 comprising a resistornetwork can be bonded to the ceramic substrate 118, which is formed onthe metal diaphragm 119. A flex circuit 112 comprises an ASIC, EMIprotection and associated circuit components. The ceramic substrate 118is bonded to the metal diaphragm and provides corrosion protection tothe metal diaphragm 119.

The flex strip 112 connects the bridge circuit 115 to a case or housing108 (e.g., a cover) and a connector portion 106. The flex circuit can beelectrically and mechanically attached to the bridge circuit by catchingthe flex circuit 112 and z-axis conductor 128 with a plastic lead frame127 which snaps around the and holds the z axis conductor and flexcircuit in place. The components can be aligned such that the conductorpath is from the bridge circuit, through the z axis conductor into theflex circuit. Such an assembly method and configuration can thereforeeliminate the need for soldering and wire bonding.

An input pressure port 122 can be provided for pressure sensing thereof,such that the input pressure port is welded to the metal diaphragm 119to thereby form the transducer apparatus 100 comprising the metaldiaphragm, the ceramic substrate the bridge circuit and the inputpressure port. FIG. 1 additionally illustrates welded joint between thepressure port 122 and diaphragm 119. A threaded portion 123 is alsodepicted in FIG. 1, along with a crimp edge 126, and a connector portion106. A case or housing 108 surrounds the aforementioned internalcomponents of transducer apparatus 100. Housing 108 can be formed from asuitable material such as plastic a light-weight and non-conductingmaterial. Note that more that one pressure port 122 or connector 106 maybe embodied with transducer apparatus 100.

Transducer apparatus 100 solves the need for a low-cost andhigh-accuracy pressure transducer that can be utilized in corrosivemedia and high-temperature applications. Transducer apparatus 100 can beformed via a ceramic-on-metal technology adapted for use as a pressuresensor design that can be constructed at a low-cost. Processes that areutilized for the formation transducer apparatus 100 include molecularbonding of ceramic to a metal diaphragm, such as, for example, metaldiaphragm 119, followed thereafter by welding of the metal diaphragm(i.e., metal diaphragm sensor) to the input pressure port. Theceramic-on-metal design provides high-accuracy and stability over anoperating temperature range of approximately 40° C. to 150° C.

Ceramic material can be molecularly bonded to the metal diaphragmutilizing an ATF (Advanced Thick Film) process. The metal diaphragm istherefore formed as a ceramic coated article having a metal core (i.e.,the metal of the metal diaphragm) and having on at least a portion ofthe surface of the metal core a coating of a ceramic. The ceramic canbe, for example, a glass ceramic, but the use of glass ceramics is notconsidered a limiting feature of the present invention. Glass ceramic ispresented herein only as an example in which the invention can beembodied via the ATF process.

A glass ceramic coating can be based on its oxide content and on thetotal weight of the coating, comprising, for example, (a) from about 8to about 26% by weight of magnesium oxide (MgO); (b) from about 10 toabout 49% by weight of aluminum oxide (Al₂O₃); and (c) from about 42 toabout 68% by weight of silicon oxide (SiO₂). Ceramic/glasses adapted foruse with the transducer apparatus 100 described herein, generallypossess high temperature re-firing capabilities (e.g., 850° C.), and areair fireable. Moreover, ceramic coated article can exhibit a compositethermal coefficient of expansion which is optimum for use in electronicdevices, and which can exhibit a low dielectric constant which allowsfor use with high frequency circuits and allows for greaterapplicability in electronic application.

Furthermore, the ceramic/glasses utilized via the ATF process thereofcan exhibit strong adhesion to the metal substrate after firing and arevery resistant to thermal stress. This avoids breakdown of the devicesformed from the ceramic coated article of this invention when sucharticles are exposed to high temperatures normally encountered in theoperation of electronic devices. This resistance to thermal stress isindeed surprising in view of the relatively large difference in thethermal coefficient of expansion of the metal substrate and the ceramicglass, and the prior teachings that the metal and coating coefficientsof expansion must be matched to produce good adhesion.

The glass/ceramic coated article thus generally comprises a metal coreand possesses on at least a portion of the surface of the metal core acoating of a glass ceramic. A general example of the ATF involves: (a)heating a metal substrate in the presence of oxygen at a firsttemperature for a time sufficient to form any amount of an oxide layeron the surfaces of the substrate; and (b) applying to all or a portionof the surfaces of the substrate a suspension comprising one or moreorganic solvents, one or more heat degradable polymeric binders and acalcined mixture of finely divided non-conductive materials comprising(i) from about 8 to about 26% by weight of MgO; (ii) from about 10 toabout 49% by weight of Al₂O₂ and (iii) from about 42 to about 68% byweight of SiO₂.

Such an ATF process additionally can include (c) heating thecoated/metal substrate combination of step (b) at a second temperaturefor a time sufficient to remove substantially all of the solvents fromthe applied suspension; and (d) heating the coated/metal substratecombination of step (c) at a third temperature for a time sufficient todegrade substantially all of the binders in the applied suspension; (c)heating the coated/metal substrate combination of step (d) at a fourthtemperature for a time sufficient to sinter the non-conductive materialto form a device comprising a metal substrate having a predeterminedpattern of glass/ceramic material bonded to one or more surfacesthereof.

The material can generally comprise (on an oxide basis): (i) from about8 to about 26% by weight of MgO; (ii) from about 10 to about 49% byweight of Al₂O₃; and (iii) from about 42 to about 68% by weight of SiO₂; (f) heat treating the device at a fifth temperature for a timesufficient to re-crystallize any residual glass contained in thematerial to any extent.

The ATF process provides for greater selectivity in the application ofthe glass/ceramic materials to specific sites on a substrate whichprovides for greater freedom in the manufacture of devices such as thetransducer apparatus 100. After processing, in accordance withembodiments disclosed herein, the coating can contain crystallizedglass/ceramic, which strongly adheres to the metal core and can besuitable as a substrate for processed induced components. An example ofan ATF process is disclosed in U.S. Pat. No. 4,794,048 entitled,“Ceramic Coated Metal Substrates for Electronic Applications,” whichissued to Oboodi et al on Dec. 28, 1988, and which is incorporatedherein by reference. Another example of an ATF process is disclosed inU.S. Pat. No. 4,997,698 entitled “Ceramic Coated Metal Substrates forElectronic Applications,” which issued to Oboodi et al on Mar. 5, 1991,and which is incorporated herein by reference.

The embodiments and examples set forth herein are presented to bestexplain the present invention and its practical application and tothereby enable those skilled in the art to make and utilize theinvention. Those skilled in the art, however, will recognize that theforegoing description and examples have been presented for the purposeof illustration and example only. Other variations and modifications ofthe present invention will be apparent to those of skill in the art, andit is the intent of the appended claims that such variations andmodifications be covered.

The description as set forth is not intended to be exhaustive or tolimit the scope of the invention. Many modifications and variations arepossible in light of the above teaching without departing from the scopeof the following claims. It is contemplated that the use of the presentinvention can involve components having different characteristics. It isintended that the scope of the present invention be defined by theclaims appended hereto, giving full cognizance to equivalents in allrespects.

1. A transducer apparatus, comprising: a metal diaphragm molecularlybonded to a ceramic material to form a ceramic surface thereof; a bridgecircuit connected to said ceramic surface of said metal diaphragm; aninput pressure port for pressure sensing thereof, wherein said inputpressure port is connected to said metal diaphragm to thereby form atransducer apparatus comprising said metal diaphragm, said bridgecircuit and said input pressure port.
 2. The apparatus of claim 1wherein said metal diaphragm is welded to said input pressure port. 3.The apparatus of claim 1 wherein said metal diaphragm and said ceramicsurface thereof operate over a temperature of range of at least 40° C.to 150° C.
 4. The apparatus of claim 1 wherein said ceramic material ismolecularly bonded to said metal diaphragm to form said ceramic surfacethereof.
 5. The apparatus of claim 1 wherein said ceramic surface bondedto said metal diaphragm comprises a ceramic substrate.
 6. The apparatusof claim 5 wherein said ceramic substrate bonded to said metal diaphragmprovides corrosion protection to said metal diaphragm.
 7. The apparatusof claim 1 wherein said bridge circuit comprises a resistor network. 8.The apparatus of claim 1 wherein an electrical circuit is formed from aflex circuit board comprising an ASIC and associated circuitry thereof.9. The apparatus of claim 8 further comprising EMI circuitry which formspart of said flex circuit.
 10. A transducer apparatus, comprising: ametal diaphragm molecularly bonded to a ceramic substrate, wherein saidmetal diaphragm and said ceramic substrate operate over a temperature ofrange of at least 40° C. to 150° C. a bridge circuit bonded to saidceramic substrate of said metal diaphragm to provide corrosionprotection to said metal diaphragm; EMI circuitry configured on saidflex circuit; an input pressure port for pressure sensing thereof,wherein said input pressure port is welded to said metal diaphragm tothereby form a transducer apparatus comprising said metal diaphragm,said ceramic substrate said bridge circuit and said input pressure port.11. A method for forming a transducer, comprising the steps of:molecularly bonding a metal diaphragm to a ceramic material to form aceramic surface thereof; connecting a bridge circuit to said ceramicsurface of said metal diaphragm; and providing an input pressure portfor pressure sensing thereof, wherein said input pressure port isconnected to said metal diaphragm to thereby form a transducer apparatuscomprising said metal diaphragm, said bridge circuit and said inputpressure port.
 12. The method of claim 11 wherein the step of connectinga bridge circuit to said ceramic surface of said metal diaphragm,further comprises the step of: welding said metal diaphragm to saidinput pressure port.
 13. The method of claim 11 wherein said metaldiaphragm and said ceramic surface thereof operate over a temperature ofrange of at least 40° C. to 150° C.
 14. The method of claim 11 whereinthe step of connecting a bridge circuit to said ceramic surface of saidmetal diaphragm, further comprises the step of: molecularly bonding saidceramic material to said metal diaphragm to form said ceramic surfacethereof.
 15. The method of claim 11 wherein said ceramic surface bondedto said metal diaphragm comprises a ceramic substrate.
 16. The method ofclaim 15 wherein said ceramic substrate bonded to said metal diaphragmprovides corrosion protection to said metal diaphragm.
 17. The method ofclaim 11 wherein said flex circuit comprises an ASIC (ApplicationSpecific Integrated Circuit).
 18. The method of claim 17 furthercomprising the step of forming said ASIC from a flex circuit.
 19. Themethod of claim 18 further comprising the steps: providing a Z-axisconductor; and forming a conductor path from said bridge circuit,through said z-axis conductor into said flex circuit.
 20. The method ofclaim 11 further comprising the step of providing a housing in whichsaid transducer apparatus, including said bridge circuit, said metaldiaphragm, said ceramic surface and said input pressure port arelocated.